The present invention relates to synthetic, wet-laid, nonwoven sheets and more particularly relates to synthetic, wet-laid, nonwoven sheets having an additive distributed in a cross-directional pattern across the sheets.
Various types of synthetic, wet-laid, nonwoven sheets such as papers and processes for making such sheets are known and are described in, for example, U.S. Pat. Nos. 2,999,788 and 3,756,908. As disclosed in U.S. Pat. No. 3,756,908, the papers produced from fibrids and floc of non-fusible, aromatic polyamides are particularly useful due to excellent thermal and electrical insulation properties.
For papers of the type disclosed in U.S. Pat. Nos. 2,999,788 and 3,756,908 and in other papers produced from synthetic fibrous stocks, it is desirable for some specialized end uses for an additive to be distributed in higher and lower additive quantities across the width of the sheet while being consistent along the sheet length, i.e., distributed in a "cross-direction" in the sheet. For example, in the manufacture of "honeycomb" structures from such papers, it is desirable for an additive or colorant to be distributed in the paper so that one face of the honeycomb contains the additive or colorant whereas the other face has a lower amount of such additive or colorant. In papers for making honeycomb and for other uses, it may be desirable for the additive to be entirely absent in some cross-directional areas of the sheet or for a particular cross-directional pattern of additive to be provided. A process is needed for producing such synthetic nonwoven sheets having additives distributed in a cross-direction in the sheet.